This invention relates generally to the acquisition and processing of optical signals derived from measuring transducers, utilized, for example, in an electro-optic instrument that detects and displays temperature from an optical temperature transducer.
Many particular techniques have been suggested for optically measuring the temperature of an object or an environment. A material that exhibits a change in some optical property is either applied directly to the object or made as part of a temperature probe, such as a probe formed on the end of an optical fiber. One such material is a phosphor that exhibits some change in its light emission as a function of its temperature in response to appropriate radiation excitation. Measuring the decay time of a phosphor emission after a pulse of exciting radiation, and the measurement of phosphor emission color chift as a function of temperature are two such methods that are described in U.S. Pat. No. 4,223,226--Quick et al. (1980). A decay time technique is also disclosed in U.S. Pat. No. 4,245,507--Samulski (1981).
Other techniques utilize varying phosphor emission intensity as a function of temperature. The emission intensity is measured as an indicator of phosphor temperature. One particular form of the intensity measuring technique having many advantages is described in U.S. Pat. Nos. 4,075,493--Wickersheim (1978) and 4,215,275--Wickersheim (1980), assigned to Luxtron Corporation, the assignee of the present application. These patents show as a preferred technique the use of a phosphor which, when excited to luminescence, emits detectable radiation within two or more distinct wavelength ranges that are optically isolatable from one another, the relative intensity of emission in these wavelength ranges varying in a known manner as a function of the temperature of the phosphor. The preferred phosphor is one that emits sharp lines of radiation upon excitation, such as those having rare earth activators. A temperature measuring system utilizing such a phosphor preferably takes the ratio of emissions within two optically separable emission bands, and it is the ratio that is a function of the temperature of the phosphor. Ratioing minimizes many sources of error in the measurement, such as changes in the excitation source intensity, phosphor characteristics over time, or changes in the optical transmission system, such as an optical fiber, that communicates the phospor emission to a detecting instrument.
Various approaches to optical temperature measurement are discussed in a published paper, which includes a description of an instrument sold by Luxtron Corporation, "Recent Advances in Optical Temperature Measurement", Wickersheim and Alves, Industrial Research/Development, December, 1979. The Luxtron instrument that has been marketed for some time utilizes an optical assembly positioned between an end of an optical fiber probe assembly and two detectors. These optics select two different groups of emission lines of the phosphor temperature sensor and direct the emission of one group of lines to one of the detectors and the other group of lines to the other of the detectors. These same optics direct ultraviolet radiation of a different wavelength into the optical fiber for exciting to emission the phosphor temperature sensor at the other end.
It is object of the present invention to provide optical multiplexing techniques for simultaneously handling multiple temperature sensors.
It is another object of the present invention to provide multiplexing and calibration techniques that are advantageous in acquiring a wide variety of optical signals originating from various types of transducers that measure temperature, pressure, flow, stress, strain and similar parameters.